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CONCLUSIONS AND RECOMMENDATIONS In summary, the soil conditions examined near the existing septic system drain field were found to be suitable. A satisfactory soil percolation rate of 5.95 min/in was observed in the shallow soil zone at the test location. The depth of ground water based on recent aquifer levels is approximately 12 to 18 feet below ground surface. The ground-water flow is to the east or east-southeast at a rate of approximately eight to 11 feet per mile. The highest recent ground-water levels for San Joaquin County were experienced in 1983 and 1999; however, depth to water in the Tracy area was not mapped for those years. Because of the percolation rate between 5.0 and 30.0 min/in encountered in the test hole, the San Joaquin County Environmental Health Department will require an eight- foot separation from the bottom of the dispersal system to ground water. Based on the anticipated depth to ground water, no modifications to standard, shallow septic systems should be required. The domestic well on the Site is inoperable; consequently, no water sample was collected as part of this study. Based on a review of San Joaquin County Environmental Health Department map of nitrate detections in nearby wells, four wells within a half-mile radius of the subject Site have been tested for nitrate; nitrate was detected in all four wells at concentrations between 0.1 and 5.0 mg/L-N. According to the DBCP map, only one well within a half- mile radius was tested for DBCP; no DBCP was detected. Based on the method and assumptions described, the nitrate loading calculation indicates that the use of on-site septic tanks and drain field systems on the Site has the potential to cause a buildup of nitrate in the aquifer of 10.5 mg/L-N for a two-bedroom house, 12.7 mg/L-N for a three-bedroom house, or 14.3 mg/L-N for a four-bedroom house. All three scenarios result in a concentration above the US EPA drinking water recommendation of 10 mg/L-N. However, based on the conservative nature of the calculation, low levels of nitrate in nearby wells, clay soil present in the area, and anticipated future sewer service in the area, it is the professional opinion of Live Oak that septic effluent from a two-bedroom home on the subject Site is unlikely to contribute substantially to a build-up of nitrate in the ground water. Use of a standard, shallow septic system (leach lines or a filter bed) should be permitted for a two-bedroom' home. If a larger home is desired, it is anticipated that the San Joaquin County' Environmental Health Department may request septic system modification for nitrate- reduction. LOGE 1910 Page 13